This option enables warnings about deprecated or problematic code and sets $VERBOSE to true. Many Ruby programmers use this option routinely to ensure that their code is clean.

This option runs the Ruby code in script. If more than one -e option is specified, their associated scripts are treated as separate lines of code. Also, if one or more -e option is specified, the interpreter does not load or run any program specified on the command line.

To enable succinct one-liner scripts, Ruby code specified with the -e option may use the Regexp matching shortcut explained later in this chapter.

This option adds the directories in path to the beginning of the global $LOAD_PATH array. This specifies directories to be searched by the load and require methods (but does not affect the loading of the program specified on the command line).

Multiple -I options may appear in the command line and each may list one or more directories. If multiple directories are specified with a single -I option, they should be separated from each other with : on Unix and Unix-like systems and with ; on Windows systems.

This option loads the specified library before running the specified program. This option works as if the first line of the program were:

require 'library'

The space between the -r and the name of the library is optional and often omitted.

This frequently used command-line argument is not a true option but simply a clever application of the -r option. It loads the module named ubygems (with no r) from the standard library. Conveniently, the ubygems module simply loads the real rubygems module. Ruby 1.9 can load installed gems without this module, so this option is only necessary in Ruby 1.8.

This Ruby 1.9 option prevents the addition of gem installation directories to the default load path. If you have many gems installed, and you are running a program that does not use those gems (or a program that explicitly manages its own dependencies with the gem method), you may find that your program startup time is reduced with this option.

These options set the global variables $DEBUG and $VERBOSE to true. Your program, or library code, used by your program may print debugging output or take other action when these variables are set.

This option displays a list of interpreter options and exits.

These are all synonyms for -w: they enable verbose warnings and set $VERBOSE to true.

This option suppresses all warnings.

This option prints the Ruby version number. If no program is specified, it exits rather than reading a program from standard input. If a program is specified, run it as if --verbose (or -w) had been specified.

These options print Ruby version number, copyright information, or command-line help and exit. --help is a synonym for -h. --version differs from -v in that it never runs a specified program.

In Ruby 1.8, this option specifies the source encoding of the script and sets the global variable $KCODE. In Ruby 1.9, it sets the default external encoding of the Ruby process and specifies a default source encoding.

Specify a code of a, A, n, or N for ASCII; u or U for Unicode; e or E for EUC-JP; and s or S for SJIS. (EUC-JP and SJIS are common Japanese encodings.)

These Ruby 1.9 options allow you to specify the default external encoding, the default internal encoding or both. The encodings string is the case-insensitive name of one or two encodings, separated by a colon. To specify just a default external encoding, simply use the name of the desired encoding. To specify two encodings, list the default external first, followed by a colon and the default internal. To specify just a default internal encoding, use a colon followed by the default internal encoding name.

Specifies a default internal encoding of UTF-8. Equivalent to --encoding=:utf-8.

This option is the digit 0, not the letter O. xxx should be between zero and three octal digits. When specified, these digits are the ASCII code of the input record separator character and set the $/ variable. This defines “a line” for gets and similar methods. -0 by itself sets $/ to character code 0. -00 is special; it puts Ruby into “paragraph mode” in which lines are separated by two adjacent newline characters.

This option automatically splits each line of input into fields and stores the fields in $F. This option only works with -n or -p looping options and adds the code $F = $_.split at the start of each iteration. See also -F.

This option sets the input field separator $; to fieldsep. This affects the behavior of split when called with no arguments. See -a.

fieldsep may be a single character or an arbitrary regular expression, without the delimiting slashes. Depending on your shell, you may need to quote or double the backslashes in any regular expression specified on the command line.

This option edits the files specified on the command line in place. Lines are read from the files specified on the command line, and output goes back to those same files. If ext is specified, a backup copy of the files is made, adding ext to the filename.

This option makes the output record separator $ the same as the input record separator $/ (see -0), so that that line ending is automatically added to text output with print. This option is intended for use with -p or -n. When used with one of those options, it automatically calls chop to remove the input record separator from each line of input.

This option runs the program as if it were enclosed in the following loop:

while gets             # Read a line of input into $_
  $F = split if $-a    # Split $_ into fields if -a was specified
  chop! if $-l         # Chop line ending off $_ if -l was specified
  # Program text here
end

This option works in Ruby 1.9 even though the global functions chop! and split are no longer available in that version of the language.

This option is often used with -e. See also -p.

This option runs the program as if it were written in the following loop:

while gets             # Read a line of input into $_
  $F = split if $-a    # Split $_ into fields if -a was specified
  chop! if $-l         # Chop line ending off $_ if -l was specified
  # Program text here
  print                # Output $_ (adding $/ if -l was specified)
end

This option works in Ruby 1.9 even though the global functions chop! and split are no longer available in that version of the language.

This option is often used with -e. See also -n.

This option parses the program and report any syntax errors, but does not run it.

These options change the current directory to dir before running the program.

When this option is specified, the interpreter preprocesses any arguments that appear after the program name and begin with a hyphen. For arguments of the form -x=y, it sets $x to y. For arguments of the form -x, it sets $x to true. The preprocessed arguments are removed from ARGV.

This option looks for the specified program file relative to the path specified in the RUBY_PATH environment variable. If it is not found there, it looks for it relative to the PATH environment variable. And if it is still not found, it looks for it normally.

This option sets $SAFE to n, or to 1 if n is omitted. See Security for more.

This option extracts Ruby source from the program file by discarding any lines before the first that starts #!ruby. For compatibility with the capital -X option, this option also allows a directory to be specified.